1. Field of the Invention
The present invention relates to gamma ray detection, and more specifically, it relates to techniques for tracking gamma rays.
2. Description of Related Art
Positron Emission Tomography (PET) is a very important tool used for medical diagnostics and research. A PET system of increased spatial resolution and efficiency will be of great impact, particularly on small animal imaging, where the features that need to be identified are in the range of millimeters.
The spatial resolution in most of the state-of-the-art PET systems is limited by two factors: 1) the dimension of the scintillating pixels used in the detector arrays, and 2) the Compton scatterings that the gamma-ray undergoes in the detector array before being absorbed in a photoelectric interaction. The use of heavy scintillators helps reduce the fraction of Compton scatterings, and the average length between scatterings, but Compton scatterings are still important.
Position sensitive semiconductor detectors, especially the double sided segmented planar detectors, are alternatives to scintillator arrays. Such detectors have the advantage of a 3D position sensitivity, and potentially superior position resolution and granularity. The introduction of the planar Ge detectors with orthogonal strip segments has allowed the development of new, compact and efficient Compton scatter imagers. These detectors are characterized by a superior energy resolution. Position sensitivity is provided by the orthogonal strip segments of around 2 mm pitch. Despite a limited segment pitch size of 2 mm, position resolution in the sub-millimeter range is demonstrated by using new waveform filtering methods. Some of the methods employed to make that possible are described in U.S. patent application Ser. No. 11/607,554, titled: “Methods for Increasing the Sensitivity of Gamma-Ray Imagers,”) filed Nov. 30, 2006, using Express Mail label number EV424773615US, incorporated herein by reference. Position sensitive detectors normally used in PET systems provide good intrinsic position resolution, but do not correct for multiple interactions caused by Compton scatterings of the 511 keV annihilation photon in the detector.